DIMM SDR SDRAM PC-100 Bus Speed Memory (RAM)

How RAM Got in Step

One thing that was discovered as computers got faster was the importance of timing. Early designs ran different components at different speeds and accepted the delay when two subsystems were out of step; this ended with the introduction of SDRAM.

What Does PC100 Mean?

The full name of the standard is PC100 SDRAM, which stands for 100 MHz Synchronous Dynamic Random Access Memory. This means that it works in time with the memory bus so that the data is always available when the processor calls for it. There are two major factors that affect the overall performance of the system:

• Latency: Also known as CAS latency, this represents the delay between a memory request and data being available on the pin. Lower latency makes for a more responsive system.
• Bandwidth: This refers to the total amount of data transmitted per second; PC100 offers 800 MB per second, while PC66 only offers 533 MB per second and PC133 SDRAM boosts the transfer rate to 1.06 GB per second.

What's the Difference Between Desktop and Laptop Memory?

While both desktops and notebooks can use PC100, they do use different form factors. There are two primary reasons for this; first, there is simply less space inside a notebook chassis, so using the physically smaller SODIMM format takes up less room on the motherboard. The second is that portable computers don't need as many advanced data protection features, so notebook modules don't need the extra pins required by registered and ECC memory; it's all non-ECC in your laptop. Both use a 64-bit interface with the same signaling voltage and data protocol.

• Desktop: These systems use a standard 168-pin SDRAM DIMM that's 133.35 millimeters long by 30.48 millimeters high and runs at 3.3 Volts.
• Laptop: Notebooks use a 144-pin SDRAM SO-DIMM that's 67.6 millimeters long by 30 millimeters high and also runs at 3.3 Volts.

Planning a Memory Upgrade

The first thing to do when planning an SDRAM memory upgrade is to determine your system capabilities. Make sure you know how much storage your motherboard can support and any chipset limitations that you might run up against. Some boards can only handle 64 MB sticks, while others can handle 128 MB and even 256 MB sticks. It's also important to check the configuration requirements as this can vary from board to board depending on the chipset. In some cases, you can only get the maximum configuration with a certain number of DIMMs, and even only if you populate specific slots. In other cases, you can just put the sticks wherever you want them. One good thing is that 168-pin DIMMs are backwards compatible in that you can put a PC133 DIMM in a PC66 motherboard and have no issues with stability.